I recently was pulling some components of a used board and ran into what i thought at first was a transistor. Testing with a meter i found a diode junction, but when i tested other lead combinations the diode junction switched to 0 ohms (both directions). After careful study, the diode switches to o ohms until you reverse the probes, then it goes back to being a diode again. Does anyone know what this is? Whatever stated it diode is in, it will not revert until the - probe is touched to the lead.

 

It is a mosfet. You can charge the gate capacitance using your probes and then the mosfet will stay on for a while until the gate discharges. It has a parasitic diode between source and drain, so that is what you measure when it is off.